In the US, Stanley Fish is one of the big punchers of the academic world, a renowned intellectual showman and top-dollar prof. In Britain, he will always be better known as Morris Zapp, one of the most memorable characters of David Lodge's campus novels, especially Changing Places (1975) and Small World (1984). In the first of these, Zapp, a ruthlessly professional professor from California, sets out to be the world's greatest Jane Austen expert (though he rather dislikes her writing). In the second, he becomes even more famous and successful by learning all the party tricks of French literary theory. Charming, intelligent and unstoppable, fuelled by egomania (though Lodge gives him private anxieties to make him sympathetic), he is openly disdainful of his muddle-headed, shabbily dressed British counterparts, who are apparently incapable of publishing the necessary paradigm-shattering books.

Lodge was happy for it to be known that Morris Zapp was Stanley Fish, and one imagines that Fish would have been happy enough too. For Zapp's real-life counterpart has always been a sharp publicity seeker, and has prospered as an intellectual controversialist. He began as a wunderkind at Berkeley ("Euphoric State University" in Changing Places) in the 1960s, making his name in his 20s with a book on the author to whom he now returns: Milton. Surprised by Sin (1967) was a sublimely self-confident debut, grabbing the greatest poem in the language, Paradise Lost, by the scruff of its neck and shaking it to life (for undergraduates and their grateful teachers, at least).

It had a simple argument, remorselessly pursued (as is Fish's way). Paradise Lost recreates in the mind of the reader "the drama of the Fall to make him fall again exactly as Adam did and with Adam's troubled clarity". Fish's triumph was to make out of common student misconceptions about the poem (isn't Satan rather magnificent? Isn't Adam admirable for joining Eve in her disobedience?) a corrective polemic. Milton tempts us into these mistakes, and many others. The errors of undergraduates less clever than Fish are made the evidence of our fallen nature.

It is a pity that Zapp disappeared from Lodge's fiction after a cameo appearance in Nice Work (1986), for Fish went on to become even more successful and even more like a creature from some satire upon academic mores. He went from professorship to professorship until he arrived at the little-known but hugely rich Duke University in North Carolina. There he became an intellectual entrepreneur, upping the profile of his new university with controversy-causing books and a series of "signings" of top-rank humanities professors. With Fish as a figurehead, Duke became the Blackburn Rovers of the academic world, spending its way up the Premiership table (though Fish himself has moved on again, to more garlands at the University of Illinois).

Fish's own output, unhampered by too much in the way of teaching commitments, burgeoned and became provoking in new ways. The very title of his defence of political correctness, There's No Such Thing as Free Speech and It's a Good Thing Too (1994), gives you the flavour. In this and such follow-ups as The Trouble with Principle (1999) he declared all intellectual activity to be rhetoric. There is no truth, only fancy argument; and the fancier the better. Value judgments are politically inspired assertions. Literary theory is fine provided you accept that it is all a game. Liberalism and humanism are fuzzy-minded self-deception. His own brand of intellectual showmanship is therefore the purest honesty.

"I don't have any principles," Fish has written. When Samuel Johnson was told of a philosophical sceptic making this claim, he remarked that when he left the room, it might be best to count the silver. So it appears a paradox that Fish is drawn to Milton, that most frighteningly principled of writers. The terminal sceptic takes on the man of absolute faith.

In fact, Fish finds Milton's renunciations very congenial. His Milton is a poet of "fierce egotism" who seeks self-subjection to the will of God. "I conceav'd my selfe to be now not as mine own person but as a member incorporate into that truth whereof I was perswaded," Milton wrote of the hardening of his Puritanism. But this is easier to say than to perform. In early poems such as "Nativity Ode" and "Lycidas", he literally silences himself - forcing himself into poetic commonplace just as his own voice seems to be taking wing. Much of Fish's new book follows Milton's exploration of "the temptation of self-love", whose "innumerable forms" he "elaborates and caresses", but must put behind him.

This Milton corrects our readerly errors even more radically than in Fish's first book, and often in a thoroughly Fish-like manner. Fish's anti-liberalism is at the heart of the demonstration. For Fish, Milton is the greatest anti-liberal writer, contemptuous of doubters in the realm of politics and religiously certain of the one, pure Protestant way. The pure heart knows God, and ambivalence is the sure sign of infected purposes. To be "conflicted", as Fish puts it, is to be lost to God.

He is often on to something. Milton was so transformed by the romantics into a bard of rebellion that it is salutary to be reminded of the wilfulness of this distortion. Much that we usually look for in literature "proceeds from error and is finally unreal" in Milton's vision. In particular, originality, the credo of the imperious imagination, sits ill with Miltonic values: humility, patience, utter dependence on God's grace. However, plenty of critics have shown this more modestly than Fish.

Fish has switched his gaze away from Paradise Lost, notably to Comus, samples of Milton's prose and Paradise Regained. The last of these has a special significance, for it dramatises Christ's temptation by Satan in the wilderness. "Temptation" is at the heart of Fish's argument here, as it was in his first book. As before, it is what the reader has to experience in order to arrive at self-renunciation: the end of the poem and Milton's creed. The reader who sticks with How Milton Works will certainly be taken through many a knotty piece of Miltonic reasoning, elegantly tied and untied by Fish.

But do you want him as your guide? Like Zapp, he has no idea of being literature's servant. He is out to hammer his truth home, recruiting Milton in a demonstration that our every likely value is defeated by his poetry. His book needs to presume that we find Milton's beliefs, and even more the sheer force of those beliefs, inimical. It never occurs to Fish that the ever-abused "reader" might share any values with Milton. Milton's poetry, properly pursued, disposes of liberal ambivalence, tolerance, originality, even individuality itself.

So this is all really satanic stuff. Even when he has a point, Fish is wrestling Milton to his cause. There is no room to consider that Milton's poetry might be wise about human weakness, and that Paradise Lost , for instance, might be more notable for its sense of tragedy than for its doctrinal correctness. There is nothing to explain why the poetry might haunt rather than batter us. Fish pursues Milton's theological convolutions, but the lucid, inescapable rhythms of much of what he quotes remind you everywhere of all the strange beauty he ignores.